Silencer

ABSTRACT

A gas flow conduit consists of inner and outer flow sections whose end portions overlap. Communication between the sections is afforded by slots in the wall of the overlapped inner section. This design controls the pattern of gas flowing through it and leads to, for example, a reduction in acoustic noise and to better gas flow measurement.

United States Patent 1191 Erskine 1 1 Mar. 27, 1973 1 SILENCER [75] Inventor: James Brian Erskine, Norton,

Stockton-on-Tees, England [73] Assignee: Imperial Chemical Industries Limited, London, England [22] Filed: July 19, 1971 [21] App1.No.: 163,835

I [30] Foreign Application Priority Data July 28, 1970 Great Britain ..36,S05/70 [52] 11.8. C1. ..18l/57,181/53,181/56, 181/63, 181/36R [51] Int. Cl. ..F0ln l/08, FOln 7/18 [58] Field of Search ..18l/35C, 47 R,46, 40, 50, 181/56, 57, 53, 60, 63, 72, 67, 36 R, 36 D [56] References Cited UNITED STATES PATENTS Primary Examiner-Robert S. Ward, Jr. Att0rneyCushman, Darby & Cushman 57 ABSTRACT A gas flow conduit consists of inner and outer flow sections whose end portions overlap. Communication between the. sections is afforded by slots in the wall of the overlapped inner section. This design controls the pattern of gas flowing through it and leads to, for example, a reduction in acoustic noise and to better gas flow measurement.

10 Claims, 7 Drawing Figures PATENTEDMARZYIQYS 3, 7 2,520

' SHEET 3 BF 3 Inventor y M d ltorney' SILENCER The present invention relates to apparatus for use as silencing, fluid mixing, and fluid flow-smoothing equipment on chemical plant.

There are very many situations in chemical industry where fast flowing streams of gases need to be handled or processed and considerable attention has to be paid to the sundry disadvantageous consequences that follow from undesirable patterns of gas flow. Audible noise is one prominent disadvantage recognized by the public at large but there are other disadvantages known to the process operator, including induced vibrations, often of low frequency, in plant equipment and the difficulty of monitoring true gas flow rates along angular or tortuous gas conduits. One way of overcoming the latter problem is to provide a straight section of conduit on the upstream side of the orifice plate but in practice it is found that such a section needs to be of very considerable length and it is not always possible or convenient to arrange this.

This invention is aimed at the provision of a gas flow conduit capable of beneficially controlling the pattern of gas flow therethrough whereby, for example acoustic noise' may be reduced or eliminated, for example in vents and in the hoods of safety suits, and/or better gas flow measurement achieved.

The present invention provides a gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and the communication between the sections being afforded by slots formed in the wall of the over-lapped terminal portion of the inner flow section, the collective area of the said slots being larger than the cross-sectional area be in either direction.

The slots may be discontinuous or may extend around the entire wall. Thus, in the case where the slots are formed in the wall of a hollow cylinder, the hollow I cylinder may be conveniently and simply formed by joining together a series of hoops, spaced apart from one another and linked by short lengths of rodding.

A further form of the invention comprises a gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and the communication between the sections being afforded by orifices formed in the wall of the overlapped terminal portion of the inner flow section, the collective area of the said orifices being larger than the crosssectional area of the flow path provided by the outer flow section, immediately adjacent to the orifices, in combination with flow monitoring apparatus which is positioned downstream of the first and second flow sections.

The flow monitoring apparatus may conveniently, for example, be an orifice plate and differential pressure cell or a pitot tube.

Another form of the invention comprises a gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and the communication between the sections being afforded by orifices formed in the wall of the overlapped terminal portion of the inner flow section, the collective area of the said orifices being larger than the crosssectional area of the flow path provided by the outer flow section immediately adjacent to the orifices, included in fluid mixing apparatus.

The present invention also provides a method of reducing or eliminating acoustic noise caused by gas flow which comprises interposing in the path of the gas flow a gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and the communication between the sections being afforded by slots'formed in the wall of the overlapped terminal portion of the inner flow section, the collective area of the said slots being larger than the cross-sectional area of the flow path provided by the .outer flow section immediately adjacent to the slots.

flow path provided by the outer flow section immediately adjacent to the slots.

The present invention also provides a method of mixing at least two fluids which comprises providing a gas flow conduit comprising first and second sections in series,'through both of which one of the fluids flows, terminal portions of the sections being in overlapping relation with annular clearance therebetween and the communication between the sections being afforded by orifices formed in the wall of the overlapped terminal portion'of the inner flow section, the collective area of the said orifices being larger than the cross-sectional area of the flow path provided by the outer flow section immediately adjacent to the orifices, and flowing a second fluid past the zone of exit of the first fluid from the orifices.

Four embodiments of the invention will now be described with reference to the accompanying drawingsin which:

FIG. 1 is a perspective view of the inner section of a gas flow conduit according to the invention,

FIG. 2 is a side elevation ofa gas flow conduit,

FIG. 3 is a schematic plan ofa gas flow conduit,

FIG. 4 is a diagram illustrating the effect of a gas flow conduit on the measurement of fluid flow rates,

FIG. 5 is a side elevation of a gas flow conduit arranged for mixing condensible fluids,

FIG. 6 is a side elevation of a gas flow conduit arranged as a vent acoustic silencer,

FIG. 7 is a side elevation of a gas flow conduit acting as an acoustic silencer for a safety suit.

Referring first to FIG. 1, one form of the inner section of a gas flow conduit consists of a hollow tube 1, a

section 2 of its wall being solid and a further section 3 of the wall being perforated with transverse slots 4. The end 5 of the tube 1 which is adjacent to the slots 4 is solid. The opposite end 6 is open.

FIG. 2 illustrates a gas flow conduit forming part of a pipe line. The conduit consists of a hollow tube 1 within the pipe line 11, a series of hoops 8 being attached to the tube by interconnecting rods 7. The final hoop 9 is solid. The collective area'of the slots formed by the hoops 8 is greater than the cross-sectional area of the annulus formed by pipe 11 around tube 1 and into which the gas emerges from the slots.

The hollow tube 1 is positioned in a neck 10 of the pipe line 11 by means of a flange 12.

In operation, a fluid, e.g. oxygen, flows in the pipe line 11 in the direction of the arrow in FIG. 2 and is forced to pass through the hollow tube 1 because of the provision of the neck 10. The fluid exits from the tube through the hoops 8.

FIG. 3 illustrates a further arrangement of a gas flow conduit forming part of a pipe line. The pipe line 11 has a section 13 of wider diameter intowhich is fitted a hollow tube 1 provided with a series of slots 4. The end 6 of the tube is open, and end 5 is solid. The collective area of the slots 4 is greater than the cross-sectional area of the annulus formed by pipe 13 around the tube 1.

In operation, fluid flows in the direction of the arrow shown in FIG. 3, encounters the solid end 5 of the tube and is forced into the widened section 13 of the pipe line 11. Theonly exit for fluid from the section 13 is into the tube 1 through the slots 4, and thence back into the pipe line 1 l downstream of the tube.

The effect of the gas flow conduit of FIG. 2 on gas flow perturbations is illustrated in FIG. 4. Twoorifice plates A and B were inserted in a pipe line, the plates being separated by a right angle bend. Measurements of a flow of oxygen were taken at each orifice plate, each of which ideally should record the same flow rate. The flow rates were plotted as shown in FIG. 4. Line A represents the theoretical and'curve B shows the actual In operation, two different fluids are flowing in lines 11 and 14 respectively in the direction of the arrows in FIG. 5. The fluid in line 14 encounters the solid end 5 of tube 1 and is forced into the widened section 13 of the tube 11 through the slots 4, where it encounters and mixes with the fluid from line 11.

One application of this method of mixing is in the dilution of a mixture of hot condensate from an ammonia pre-heater and saturated steam with more saturated steam before return to the system boiler. We have found that the amplitude of vibration of the diluted fluid flow is up to 10 times lower using this method of mixing compared with conventional methods of mixing, e.g., simple mixing through open ended pipes in the form of tee junctions or concentrically arranged pipes.

FIG. 6 illustrates an arrangement of a gas flow conduit acting as a vent acoustic silencer. The hollow tube 1 is provided with slots 4, a solid end 5 and, up stream from the slots, with a pressure reducing valve 15. The hollow tube is inserted in a vent 16 which is open to atmosphere, the hollow tube being positioned so that the 7 slots 4 are open to the atmosphere. The collective area plot obtained. Clearly, wide fluctuations occurred in the readings at each orifice plate. Gas flow conduits according to the invention were fitted on the upstream side of each orifice plate and readings of oxygen flow were again taken. Curve C shows the plot of these readings showing that the conduits have considerably reduced the fluctuations caused by the perturbations and brought the readings very close to the theoretical.

It was found that prior to insertion of gas flow conduits straight lengths of pipe at least 60 pipe diameters long had to be provided .on the upstream side of the orifice plates in order to ensure reasonably accurate.

readings. After provision of gas flow conduits straight lengths of pipe of 16 pipe diameters length were fully the cross-sectional area of the annulus formed by pipe 13 around the tube 1.

of the slots is greater than the cross-sectional area of the annulus formed by the vent 16 around the tube 1.

This form of silencer'has been found to reduce the acoustic noise of a'fluid flow by up to 25 db more than conventional silencers and moreover has been found to operate at much higher temperatures than conventional silencers, because conventional sound absorbtion materials, e.g. glass wool and stillite, suffer damage at high temperatures and in a system which can be saturated with water (either carried in-a gas or from rain) these materials tend to collapse and so become ineffective.

FIG. 7 illustrates an arrangement of a gas flow conduit acting as an acoustic silencer in the plastic hood of a safety suit, such as might be used in a dangerous atmosphere. The flexible tubing 1 enters the hood 17 of a safety suit and it is provided-with slots 4 and a solid end 5 This'silencer greatly increases the time for which the hood can be comfortably worn. In a conventional safety suit, air fed to the hood through the open end of a flexible tube causes considerable acoustic noise which very quickly discomforts the wearer of the hood. In a typical situation, the hood cannot'be worn for more than an hour at a time and the hearing of the wearer may be affected for some time thereafter. Fitting the silencer shown in FIG. 7 to the hood increases the length of time. for which the hood can be worn without discomfort by 4 to 8 hours.

I claim:

1. A gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and slots formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said slots being larger than the crosssectional area of the flow path provided by the outer flow section immediately adjacent to the slots.

2. A gas flow conduit as claimed in claim 1 wherein the first flow section comprises a cylindrical pipe and the second flow section comprises a hollow cylinder positioned within the pipe and with one end blanked off and with slots in its wall.

3. A gas flow conduit as claimed in claim 1 wherein the slots are discontinuous around the wall of the inner flow section.

4. A gas flow conduit as claimed in claim 2 wherein a Series of hoops joined together form the hollow cylinder, the hoops being spaced apart and linked by short rodding.

5. A gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween, and orifices formed in the wall of the overlapped terminal portion of the inner flow section affording communication between, the sections, the collective area of the said orifices being larger than the cross-sectional area of the flow path provided by the outer flow section immediately adjacent to the orifices, in combination with flow monitoring apparatus which is positioned downstream of the first and second flow sections.

6. A gas flow conduit as claimed in claim 5 wherein the flow monitoring apparatus is an orifice plate and differential pressure cell or a pitot tube.

7. A gas'flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween, and orifices formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said orifices being larger than the cross-sectional area of the flow path provided by the outer flow section, immediately adjacent to the orifices, included in-fluid mixing apparatus.

8. YA method of reducing or eliminating acoustic noise caused by gas flow which comprises interposing in the path of the gas flow a gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and slots formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said slots being larger than the cross-sectional area of the flow path provided by the outer flow section immediately ad- 10 jacent to the slots.

9. A method of controlling gas flow along a conduit which comprises causing the gas to flow through a gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and slots formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said slots being larger than the crosssectional area of the flow path provided by the outer flow section immediately adjacent to the slots.

10. A method of mixing at least two fluids which comprises providing a gas flow conduit comprising first and second sections in series, through both of which one of the fluids flows, terminal portions of the sections being in overlapping relation with annular clearance therebetween, orifices formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said orifices being larger than the cross-sectional area of the flow path provided by the outer flow section immediately adjacent to the orifices, and flowing a second fluid past the zone of exit of the first fluid from the orifices. 

1. A gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and slots formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said slots being larger than the crosssectional area of the flow path provided by the outer flow section immediately adjacent to the slots.
 2. A gas flow conduit as claimed in claim 1 wherein the first flow section comprises a cylindrical pipe and the second flow section comprises a hollow cylinder positioned within the pipe and with one end blanked off and with slots in its wall.
 3. A gas flow conduit as claimed in claim 1 wherein the slots are discontinuous around the wall of the inner flow section.
 4. A gas flow conduit as claimed in claim 2 wherein a series of hoops joined together form the hollow cylinder, the hoops being spaced apart and linked by short rodding.
 5. A gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween, and orifices formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said orifices being larger than the cross-sectional area of the flow path provided by the outer flow section immediately adjacent to the orifices, in combination with flow monitoring apparatus which is positioned downstream of the first and second flow sections.
 6. A gas flow conduit as claimed in claim 5 wherein the flow monitoring apparatus is an orifIce plate and differential pressure cell or a pitot tube.
 7. A gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween, and orifices formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said orifices being larger than the cross-sectional area of the flow path provided by the outer flow section, immediately adjacent to the orifices, included in-fluid mixing apparatus.
 8. A method of reducing or eliminating acoustic noise caused by gas flow which comprises interposing in the path of the gas flow a gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and slots formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said slots being larger than the cross-sectional area of the flow path provided by the outer flow section immediately adjacent to the slots.
 9. A method of controlling gas flow along a conduit which comprises causing the gas to flow through a gas flow conduit comprising first and second flow sections in series, terminal portions of the sections being in overlapping relation with annular clearance therebetween and slots formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said slots being larger than the cross-sectional area of the flow path provided by the outer flow section immediately adjacent to the slots.
 10. A method of mixing at least two fluids which comprises providing a gas flow conduit comprising first and second sections in series, through both of which one of the fluids flows, terminal portions of the sections being in overlapping relation with annular clearance therebetween, orifices formed in the wall of the overlapped terminal portion of the inner flow section affording communication between the sections, the collective area of the said orifices being larger than the cross-sectional area of the flow path provided by the outer flow section immediately adjacent to the orifices, and flowing a second fluid past the zone of exit of the first fluid from the orifices. 